My kids really got into it as well. And I had the same issue with DS6 - once he got to something he didn't know he wanted us to teach it to him right away. Not sure how it calibrates - it ramped him up pretty quickly to stuff at DD10's level at which point he became frustrated.

However, I was able to get him to try Dreambox with the suggestion it would help him to learn how to play Prodigy better. ;-)